In a nonvolatile memory, it is becoming difficult to scale down a floating gate (FG) type flash memory or a metal/oxide/nitride/oxide/silicon (MONOS) type flash memory. Therefore, scaling-down using an operation principle different from these memories has been continuously looked for. Nonvolatile memories having various structures, such as a ferroelectric random access memory (FeRAM), a resistive random access memory (ReRAM), a phase change random access memory (PCRAM), a magnetic random access memory (MRAM), or a three-dimensional memory have been examined.
Among these memories, ferroelectric memories such as FeRAM, FeFET (ferroelectric field effect transistor), FTJ (ferroelectric tunnel junction), ChainFeRAM (ferroelectric random access memory) etc. had the following problems. That is, the ferroelectric memories include a material difficult to handle, such as lead, and reduction in thickness of the Ferroelectric memories was difficult due to a size effect. Therefore, it was difficult to put the Ferroelectric memories into practical use except the FeRAM for a limited purpose, such as radio frequency identification (RFID) cards including a small-scale FeRAM for low power consumption.
In such a deadlock, a hafnium oxide film has been reported as a ferroelectric film not containing lead, not difficult to make a thin film thereof, capable of low voltage operation, that is, low power consumption operation, and capable of holding a record for a long time. It is expected to realize the Ferroelectric memories having a large capacity by using this hafnium oxide film.